Transducers can be utilized in a broad range of measurement applications and corresponding environmental conditions. In certain transducers, piezoresistors coupled to a diaphragm may be used to measure a pressure. The piezoresistors may be conventionally arranged as a Wheatstone bridge. Upon the application of pressure, the sensor's diaphragm deflects slightly which induces strain onto the piezoresistors. The piezoresistors respond to this strain by a change of resistance. A Wheatstone bridge configuration, as shown in FIG. 1, typically includes four piezoresistors that are arranged on the diaphragm such that two piezoresistors are put in tension while the other two piezoresistors are placed in compression. This way, two piezoresistors increase in value, while the other two piezoresistors decrease in value by the same or similar amount. By connecting the piezoresistors under tension on opposite arms of the Wheatstone bridge, and by similarly connecting the piezoresistors under compression on the other opposite arms of the Wheatstone bridge, the output of the Wheatstone bridge can produce a voltage which is proportional to the applied pressure.
In a typical pressure measurement application, the transducer is coupled to external instrumentation for reading the associated pressure signals generated by the transducer. The instrumentation can receive and condition the output signal, digitize the received signal, etc. Given the many different measurement applications, a variety of external instrumentation may be designed and interfaced with the pressured transducer for a given application. For optimum sensing performance, it can be desirable to adjust the design variables of the pressure transducer to match those of the instrumentation, or vice-versa.
One of the primary design variables of an electrical device is the impedance of the unit, as measured from the input terminals (input impedance) or output terminals (output impedance). Input impedance requirements may be derived from a need to limit the current or power draw of a unit, due to heating issues or limitations of the driving power source. Output impedances may have different design goals depending on the device end-use, such as impedance matching or bridging to control power or voltage transfer. In many fields, particularly semiconductor fabrication, impedance matching may be complicated by the need to design for impedance at a very early stage of production. While resistors can often be manually inserted into an electrical network to vary impedance at different locations, these resistors will most likely have different secondary properties than the circuit elements directly fabricated into an electrical network via semiconductor fabrication processes. For example, temperature-dependent behavior, resistance to external electrical fields, etc. may differ depending on the method and material used to vary the impedance.
To maintain tolerance and consistency, the impedance is typically set very early in the fabrication process, which can limit flexibility and create overhead as products requiring different impedance ranges are generally manufactured using separate production lines. A method to control the impedance of electrical networks, while following standard semiconductor fabrication would provide significant benefits in cost reduction and production efficiency.